From 85f409a7e7befdc20ca98b4e5cb9c98f1019ec2b Mon Sep 17 00:00:00 2001
From: Jon Gilkison <jon@interfacelab.com>
Date: Fri, 7 Jun 2024 09:34:12 +0700
Subject: [PATCH] Add support for the `vips_gamma()` function via a new func
 `Gamma()` on `ImageRef` (#433)

* Add support for vips_gamma() function for adjusting the gamma of the image

* Add support for vips_gamma() function for adjusting the gamma of the image

* Fix test for gamma
---
 vips/conversion.c  |  6 +++++-
 vips/conversion.go | 11 +++++++++++
 vips/conversion.h  |  2 ++
 vips/image.go      | 11 +++++++++++
 vips/image_test.go | 10 ++++++++++
 5 files changed, 39 insertions(+), 1 deletion(-)

diff --git a/vips/conversion.c b/vips/conversion.c
index 00fc1b08..878e8081 100644
--- a/vips/conversion.c
+++ b/vips/conversion.c
@@ -235,7 +235,7 @@ int crop(VipsImage *in, VipsImage **out, int left, int top,
   if (n_pages <= 1) {
     return vips_crop(in, out, left, top, width, height, NULL);
   }
-  
+
   int in_width = in->Xsize;
   VipsObject *base = VIPS_OBJECT(vips_image_new());
   VipsImage **page = (VipsImage **) vips_object_local_array(base, n_pages);
@@ -374,3 +374,7 @@ int replicate(VipsImage *in, VipsImage **out, int across, int down) {
 int grid(VipsImage *in, VipsImage **out, int tileHeight, int across, int down){
   return vips_grid(in, out, tileHeight, across, down, NULL);
 }
+
+int adjust_gamma(VipsImage *in, VipsImage **out, double g) {
+  return vips_gamma(in, out, "exponent", g, NULL);
+}
diff --git a/vips/conversion.go b/vips/conversion.go
index 072623c0..0738727d 100644
--- a/vips/conversion.go
+++ b/vips/conversion.go
@@ -507,3 +507,14 @@ func vipsGrid(in *C.VipsImage, tileHeight, across, down int) (*C.VipsImage, erro
 	}
 	return out, nil
 }
+
+func vipsGamma(image *C.VipsImage, gamma float64) (*C.VipsImage, error) {
+	incOpCounter("gamma")
+	var out *C.VipsImage
+
+	if err := C.adjust_gamma(image, &out, C.double(gamma)); err != 0 {
+		return nil, handleImageError(out)
+	}
+
+	return out, nil
+}
diff --git a/vips/conversion.h b/vips/conversion.h
index 5cb2d361..ac92c596 100644
--- a/vips/conversion.h
+++ b/vips/conversion.h
@@ -66,3 +66,5 @@ int is_16bit(VipsInterpretation interpretation);
 int replicate(VipsImage *in, VipsImage **out, int across, int down);
 
 int grid(VipsImage *in, VipsImage **out, int tileHeight, int across, int down);
+
+int adjust_gamma(VipsImage *in, VipsImage **out, double g);
diff --git a/vips/image.go b/vips/image.go
index e0f5ab0a..82d5fac2 100644
--- a/vips/image.go
+++ b/vips/image.go
@@ -1304,6 +1304,17 @@ func (r *ImageRef) Linear1(a, b float64) error {
 	return nil
 }
 
+// Adjusts the image's gamma value.
+// See https://www.libvips.org/API/current/libvips-conversion.html#vips-gamma
+func (r *ImageRef) Gamma(gamma float64) error {
+	out, err := vipsGamma(r.image, gamma)
+	if err != nil {
+		return err
+	}
+	r.setImage(out)
+	return nil
+}
+
 // GetRotationAngleFromExif returns the angle which the image is currently rotated in.
 // First returned value is the angle and second is a boolean indicating whether image is flipped.
 // This is based on the EXIF orientation tag standard.
diff --git a/vips/image_test.go b/vips/image_test.go
index 42a990c2..9c6090bc 100644
--- a/vips/image_test.go
+++ b/vips/image_test.go
@@ -1180,6 +1180,16 @@ func TestImageRef_SetPages(t *testing.T) {
 	require.Equal(t, 3, image.Pages())
 }
 
+func TestImageRef_SetGamma(t *testing.T) {
+	Startup(nil)
+
+	image, err := NewImageFromFile(resources + "png-24bit.png")
+	require.NoError(t, err)
+
+	err = image.Gamma(1.0 / 2.4)
+	require.NoError(t, err)
+}
+
 // TODO unit tests to cover:
 // NewImageFromReader failing test
 // NewImageFromFile failing test